In a radio system subscriber equipment communicates with base stations. During communication the subscriber equipment transmits bursty signals to the base station through an antenna. Between bursts the transmitter is not transmitting. A major part of total energy in the subscriber equipment is consumed by the transmitter. The high energy consumption still increases the longer the transmitter is continuously transmitting or the more frequently the bursts are transmitted. For example, in GSM (Global System for Mobile communication) or GPRS (General Packet Radio Service) radio systems the subscriber equipment can use multiple slots during transmission, and the general trend is towards supporting a higher number of slots for one user.
The high energy consumption has obvious disadvantages in the subscriber equipment. The power amplifier consumes more current, resulting in harmful heating of not only the power amplifier but also the whole subscriber equipment. The excess heating may cause deviation from nominal operation of components, which is harmful to the communication in the radio system.
If subscriber equipment supports single timeslot transmission in uplink direction, it may have been designed to withstand power consumption that represents single timeslot case. When multiple timeslots are to be supported the power consumption is significantly higher and may cause severe problems e.g. due to excess heat. Additionally, the increased energy consumption empties the battery of the subscriber equipment faster, leading to a more frequent need of loading and, in lack of that, to loss of operation.
To overcome the problems with excess heat in the use of multiple timeslots, a simple approach is to divide the used power with number of used timeslots in uplink transmission. This approach leads to equal power consumption when compared to single timeslot case with full power. However, this approach affects performance range as the user equipment always operates with decreased output power when multislot operation is enabled. In addition to that the scheme is suboptimal as it does not take the discontinuity of transmission into account.
When a radio link is utilized to carry packet data traffic, the transmission occurs typically in short bursts. Because of bursts it is possible to use higher peak power levels as the average power level remains low. The average power levels depend on the application and the data profile. In a typical application data is sent in shorter bursts with inactivity periods in the middle of the data transfer. This discontinuous nature can be taken into account in tuning the power level of subscriber equipment. However, there are also applications that involve longer continuous transmission, in which case the average power levels is closer to peak power levels. For these applications, if activity of transmission is taken into account in power reduction, the average power levels also decrease.